In petroleum refining, the crude oil systems employed as feedstocks are prone to produce material that deposits and accumulates upon the surfaces of heat transfer equipment contacted therewith resulting in the fouling of petroleum process equipment. In normal, continuous use, for example, the heat exchangers used in almost all crude oil unit processes suffer gradually increasing losses in efficiency, heat transfer, pressure drop, and throughput owing to deposition of material on the inner surfaces thereof. Consequently, crude oil process units must be periodically shut down and the deposits removed or the units replaced. Such fouling of heat exchangers, and also such equipment as furnaces, pipes, reboilers, condensers, compressors, auxiliary equipment, and the like, is costly by reason of the loss of production time and the man hours required for dissassembly, cleaning and reassembly of unit process equipment components. The equipment is usually fabricated of carbon steel, stainless steel, or aluminum.
The fouling is generally attributed to the presence of unstable components, such as oxidized derivatives of hydrocarbons, the inorganic impurities present in hydrocarbon fractions, the presence of olefinic unsaturated hydrocarbons or their polymeric derivatives, or the like. Thus, almost all crude oil and fractions thereof, as well as process cuts prepared from such, contain minor amounts of readily oxidized and oxidizable hydrocarbon constituents. Furthermore, almost all crude oil contains small amounts of dissolved oxygen, sulfur and metals, in a free and/or chemically combined state. If chemical and/or thermal treatment is involved, the olefinic substitutes may be polymerized.
The use of phosphate and phosphite thio esters as additives to mineral hydrocarbon mixtures employed as refinery feedstocks has heretofore been proposed. Thus, Wolff et al. in U.S. Pat. No. 3,647,677 teach triethyl thiophosphite as a crude oil additive to retard coke formation. However, triethyl thiophosphite is inferior compared to mono and diethyl thiophosphites as additives to crude oil for purposes of suppressing fouling of refinering equipment during crude oil refining. Furthermore, mono and diethyl thiophosphites unexpectedly are found to reduce fouling in previously fouled refining systems when added to crude oil being refined.
So far as known to us no one has heretofore ever employed mono and di thiophosphate and/or thiophosphite esters and amine salts thereof as antifoulant additives in crude oil materials. Such phosphorus thio esters, and amine salts thereof, have now been found characteristically to display surprising and very useful antifoulant activity in crude oil materials. Not only do these materials inhibit and supress, and even prevent, fouling when in crude oil materials, but also they unexpectedly appear to reduce the fouling in previously used and fouled crude oil refinery processing equipment. Such additives in combination can be considered to be arguable synergistic in some of these effects, and applications, as those skilled in the art will appreciate. The art of reducing fouling in refining streams is very complex and the reasons why a particular antifoulant system works to reduce fouling effectively in some mineral hydrocarbon mixtures, but perhaps not in others, are not now known.